Stressed parents, squirming kids, expensive prepping for standardized tests -- welcome to the world of applying to kindergarten.

Yes, kindergarten. Thousands of 4-year-olds across the country spend an hour every Saturday or Sunday, sometimes both, with a tutor who helps them with analogies, comprehension and pattern-recognition.

Their goal -- their parents' goal -- is a school like NEST+m on the Lower East Side of Manhattan in New York City. Neither a posh private school nor a charter school, NEST+m is a public school for the "gifted and talented." It goes from kindergarten through high school and currently boasts a 100 percent graduation rate. If you get in for kindergarten, you're in for the rest of the way through high school.

At an age when many children are not reading at all, NEST+m kindergarteners have math in the morning, science before lunch, then mandatory Mandarin Chinese in the afternoon.

In New York City, a single hour-long test, the Otis-Lennon School Ability Test (OLSAT), determines entrance to Gifted and Talented (G&T) programs at kindergarten.

"For those of us who can't afford private school, we have no choice," Lee Berman, a parent who prepped his young daughter Elaina Berman for the OLSAT, told "Nightline" anchor Cynthia McFadden.

He added, "how well they do on this will determine how they do for the rest of their educational career into middle school and then high school and beyond."

Last year, more than 12,000 children took the test in New York City alone. Approximately 4,000 scored at least in the 90th percentile, and 1,000 scored in the 99th. That vastly exceeds the number of total spots; at NEST+m there were 106 seats. In New York City, every year there are fewer than 300 spots in the system's most elite Gifted and Talented schools. So all the kids who score in the 99th percentile are put into a lottery for these precious few spots.

Thirty-seven states have a mandate to have gifted programs in their public schools. New York City has, by far, the biggest program. Yet testing for giftedness is always a thorny issue.

In his widely acclaimed book "Nurture Shock," author Po Bronson argues that tests for giftedness and talent at age four are not accurate predictors of future academic success. In 73 percent of cases, he says, the prediction didn't hold: kids who aced the test at four were not scoring at the same advanced levels in high school, while other kids were.

New York City Schools Chancellor Dennis Walcott disagrees and says he is confident the tests work.

"We've done a lot of research and analysis to make sure both that the test is at a certain level of rigor" and that "the tests are not biased," he said.

He added that the majority of students at NEST+m stay and do well in the G&T program.

"I would never qualify for [NEST+m]," Walcott admitted. "Plain and simple. Just put that on the public record: I would never qualify. And probably even now as the Chancellor I wouldn't qualify for this school."

Bright Kids NYC One of Many OLSAT Prep Firms

A whole industry of test-prep companies has cropped up around the kindergarten entrance process. Bige Doruk is the founder of Bright Kids NYC, which tutors kids and publishes textbooks of sample tests. She noted the long-term benefits of her service: "[We teach them] how to take any test, because multiple-choice tests go on and on and on in our lives."

Her company tailors a learning program to each student, working on recognizing colors, numbers, letters and patterns. Their goal is to turn 4-year-old tykes into avid test takers.

"We're in a system of tests," she said. "They younger they learn, actually, they do get better at testing."

Her own young son Finn Olsen is even preparing to take the test.

"Child number two," Doruk said, "who has ants in his pants all the time."

For private tutoring, she charges parents $165 per hour and up. Most parents who decide to go the tutoring route end up spending thousands of dollars to prep their four-year-olds.

Walcott conceded that while he believes the tests are fair, he does worry that plenty of families won't be able to afford the prep courses.

"It bothers me," he said, "But the reality is we all prepare in different ways for what those experiences will be, whether it's in a job or whether it's in school ... even at four. We are a competitive society."

Nova Hall decided to enroll her daughter in Bright Kids NYC. She was trying to get her 7-year-old son, Hayden, and 4-year-old daughter, Savannah, into the G&T program. If Savannah tested in, her brother would have a greater chance of getting in, because there are fewer available slots in higher grades.

"I think it's good that we're going to do this prep course," Hall said, "because it'll help us clarify and feel more confident."

Her husband, Jonathan, agreed.

"I just thought it would be as simple as: they take a test to see if they can handle the curriculum," he said, "and if they do well, they get offered a place. But apparently, it's not quite that simple."

Another client was Lee Berman. In his mind, aiming his daughter, Elaina, at G&T -- and giving her an advantage in getting there -- is simply good parenting.

"We wanted to be able to give her every opportunity to excel," he said. "She's a brilliant child. The school system here in New York City has a program for children who learn differently, who are able to excel above the regular standard. What parent wouldn't want to give their child the opportunity to participate in that?"

The tutoring begins with an assessment conducted in mock test conditions. Sitting still is an issue for lots of the kids.

"The biggest battle is getting them to sit and get comfortable," said Doruk. "As children like routine, every week at the same time the teacher comes. It's no different than every week there is a piano lesson."

"One of the things that we believe in is creating as many options for parents to choose from [as possible]," said Chancellor Walcott. "As part of those options, we want gifted and talented programs ... where students have to test at a certain percentile level to qualify. ... So for those students who are at the 90th percentile, they're able to qualify for a Gifted & Talented program in their particular district. Those who qualify at the 97th percentile and above, they would qualify for those few city-wide programs."

Which doesn't mean you actually get in.

Even scoring 99 percent, Walcott said, "it's still not a guarantee. There isn't a guarantee."

To see how Savannah, Elaina and Finn did, watch "Nightline" tonight at 11:35 p.m. ET.